Methyl cyanoacrylate (MCA) and other cyanoacrylates are well known chemical products which have found wide use as adhesives for both general and medical purposes. The ability of the alkyl 2-cyanoacrylates to polymerize rapidly at room temperature in the absence of a solvent or added catalyst has resulted in the use of this class of monomers for surgical application. 2-cyanoacrylate monomers have been used as physiological adhesives in bronchial closure, the anastomosis of small arteries, intestinal anastomosis and cutaneous lacerations. Methyl cyanoacrylate has also found application in the field of permanent sterilization of mammalian females including human females. Sterilization of the female is accomplished by introduction of small quantities of MCA into the fallopian tubes where contact with body moisture polymerizes the MCA and blocks the fallopian tube. With passage of time, fibrous tissue growth replaces the MCA and permanent sterilization results. This latter use and procedure is described in U.S. Pat. Nos. 3,822,702 and 3,948,259.
For some of the medical applications of the cyanoacrylates, it is desirable that there be some means for inspecting the result of the surgical operation without the need for surgically reopening the patient. For instance, in the anastomosis of arteries or intestines, it is desirable to have some means for non-intrusively inspecting the joined tubes in order to verify that a proper weld has taken place without blockage of the tube. Conversely, where MCA is used to sterilize females, it is desirable to inspect the polymer plug to insure that tube blockage has been successfully accomplished.
Radiopaque cyanoacrylate compositions are also useful for the general adhesive applications to which cyanoacrylates are put, such as the bonding of metal, plastic or ceramic parts. Radiopacity of such compositions allows inspection of the integrity of the joined seam. For instance, in the manufacture of electronic microchips it has been suggested that MCA may be a useful adhesive for joining contact leads to the chips. Since a major failure mode of electronic chips occurs at the chip-lead interface, it would be advantageous if such cyanoacrylate adhesives were radiopaque so that the weld could be examined.
If the cyanoacrylate ester is made radiopaque, the desired inspection may be accomplished by x-ray of the affected area. However, the polymerization properties which make cyanoacrylate esters useful in medical and other applications have heretofore prevented formulation of radiopaque compositions. The highly unstable cyanoacrylate esters polymerize under many conditions, including exposure to even trace amounts of moisture, oxygen, heat, high energy radiation and active organic sites to note a few. As a result, many of the known radiopaque materials commonly used in other applications cannot be incorporated into the monomer as a radiopaque additive for cyanoacrylate esters. Most radiopaque materials reduce the stability of the esters and, in some cases, even initiate polymerization thereof. In particular, it has been found that organic iodo compounds commercially available as x-ray screening agents are frequently available as sodium salts of a carboxylic acid or as compounds containing primary or secondary amino groups. These materials are not stable to cyanoacrylates and cause polymerization thereof.